1. Field of the Invention
The present invention relates to a writing implement. In this invention, the term [front] means a closed side of a cap and a pen tip side of the main body of the writing implement, while the term [rear] means an opened side of the cap and an ink tank side of the main body of the writing implement.
2. Description of the Background Art
Referring to a writing implement of this type, conventionally, in Japanese Utility Model Unexamined Publication No. JP-UM-A-2-144488, there is disclosed a cap mounting structure of the writing implement, in which the cap including an inner cap therein is mounted on a leading end portion of a barrel including a pen tip to thereby keep interior of the cap in air tight manner, wherein the inner cap is formed of soft elastic resin material and a ring-shaped projection is provided on the leading end face of the barrel and/or the end face portion of the inner cap which, when the cap is mounted onto the barrel, they are pressed against each other.
With use of the cap mounting structure disclosed in the above-mentioned JP-UM-A-2-144488, there is a fear that, when the cap is mounted, the pen tip can be contacted with the ring-shaped projection (airtight seal portion) on the end face of the inner cap to thereby cause ink to adhere to the ring-shaped projection and thus stain the ring-shaped projection or to thereby damage the ring-shaped projection and thus cause poor air tightness.
Especially, if the ink adheres to the ring-shaped projection, there is a fear that the ink adhered to the ring-shaped projection, as the cap is mounted onto the barrel, can adhere to the barrel and thus, when a user holds the barrel with a hand, the ink can adhere to the hand to thereby stain the hand.
Also, with use of the cap mounting structure disclosed in the JP-UM-A-2-144488, since the airtight seal portion is formed in the front end face of the barrel and the airtight seal portion is exposed to the outside, there is a fear that the airtight seal portion can be damaged by accident to thereby cause a poor airtight condition.
Further, with use of the cap mounting structure disclosed in the JP-UM-A-2-144488, in order to prevent the air in the interior of the inner cap from being compressed in the cap mounting operation, there is formed a notch in the ring-shaped projection for fixing the cap to the barrel. Thus, the cap mounting structure disclosed in the JP-UM-A-2-144488 provides a structure in which the air existing in the interior of the inner cap flows through a clearance between the outer surface of the barrel and the inner surface of the cap and is discharged to the outside from the opening end portion of the cap. However, since the clearance between the outer surface of the barrel and the inner surface of the cap cannot be set so large actually, there is a fear that, when the cap mounting operation is performed suddenly, the pressure air (compressed air) within the cap cannot be sufficiently discharged to the outside, thereby causing the pressure air to flow into the inside of the barrel; or, when a cap removing operation is carried out suddenly, the air existing within the cap can be decompressed, whereby the ink can leak out from the pen point side.